Glued Laminated Timber Beams Research Articles

Metamodel assisted optimization of glued laminated timber beams by using metaheuristic algorithms

An efficient use of the raw material in glued laminated timber (GLT) beams is commonly achieved by inserting lamellas of lower quality in less stressed areas, usually in the middle of a beam. But, this rather simple method leaves room for improvement. In particular, the morphology of a board and its location in the beam setup is significant, since only this information and the actual loading situation allows a proper evaluation of weaknesses. Therefore, a new optimization method was developed, able to take mechanical property distributions as well as the occurring stress states within each wooden board into account.Subsequent to an automatic knot reconstruction and determination of effective local stiffness distributions of all boards, the beams are analyzed using a finite element (FE) model. This information is further exploited to find optimal beam setups out of a sample of boards. However, as the complexity of this optimization task quickly increases with the number of boards, metaheuristic optimization algorithms were developed. Additionally, the evaluation of the computationally expensive FE model is bypassed by a metamodel, capable of approximating the desired performance parameter of any beam. Comparing the various optimization approaches to common GLT beam production methods, maximum deflection can be reduced by 15%–20%.

Stochastic engineering framework for timber structural elements and its application to glued laminated timber beams

Due to the natural growth process of trees, wooden boards show a high amount of random fluctuation in their mechanical properties. Currently, in engineering practice, a homogeneous material behaviour is assumed within wooden boards and uncertainties in loading and load-bearing capacity are considered through design procedures based on partial safety factors. These partial safety factors are not directly linked to the individual mechanical behaviour of the considered structural system/element. Thus, a stochastic framework opening up the possibility to establish such links, by combining structural analysis tools with probabilistic descriptions of wooden boards, could be an important step in timber design, also to improve the competitiveness of wood against other building materials.In this study, a framework able to consider the impact of random stiffness fluctuations of wooden boards on the performance of glued laminated timber (GLT) is presented. A 2D finite element model is employed to depict the interactions between individual laminations. It is tightly integrated into a commercial robustness analysis and optimisation software package.The mechanical properties of each board are obtained on basis of measurements collected during the grading process and are condensed into so-called stiffness and strength profiles. Based thereon, a probabilistic material model is developed for the random generation of an arbitrary number of stiffness and strength profiles. On basis of the probabilistic material model and the mechanical FE model, the sensitivity to changes in the design can be explored. Subsequently, an adaptive response surface approach leads to the optimal design parameters of the user-defined structure.An exemplary application scenario shows the workflow for determining the optimum hole dimensions and location in a GLT beam. The material model indicates large scatter in the mechanical properties, leading to conservative results. Nonetheless, and although only bending failure of GLT beams and no finger joints are taken into account, the example shows the strengths of the employed workflow from sensitivity analysis to best designs.

Determining the Dynamic Increase Factor for Glued-Laminated Timber Beams

AbstractThis paper presents the results from an experimental program that investigated the flexural behavior of glulam beams subjected to dynamic loading. A total of thirty-eight beams consisting o...

Experimental study on glued laminated timber beams with well-known knot morphology

Nowadays, the impact of knots on the failure behaviour of glued laminated timber (GLT) beams is considered by subjecting the single lamellas to a strength grading process, where, i.a., tracheid effect-based laser scanning is used to obtain information about knot properties. This approach single-handedly defines the beam’s final strength properties according to current standards. At the same time, advanced production processes of such beams would allow an easy tracking of a scanned board’s location, but, at this point, previously obtained detailed information is already disregarded. Therefore, the scanning data is used to virtually reconstruct knot geometries and group them into sections within GLT beams. For this study, a sample of 50 GLT beams of five different configuration types was produced and tested under static four-point-bending until failure. As for each assembled lamella the orientation and position within the corresponding GLT beam is known, several parameters derived from the reconstructed knots can be correlated to effective GLT properties. Furthermore, the crack patterns of the tested beams are manually recorded and used to obtain measures of cracks. A detailed analysis of the generated data and their statistical evaluation show that, in the future, dedicated mechanical models for such timber elements must be developed to realistically predict their strength properties. A potential approach, using fluctuating section-wise effective material properties, is proposed.

Stochastic model for predicting the bending strength of glued-laminated timber based on the knot area ratio and localized MOE in lamina

The aim of this study was to develop a stochastic model for predicting the bending strength distribution of glued-laminated timber (GLT). The developed model required the localized modulus of elasticity (MOE) and tensile strengths of laminae as input properties. The tensile strength was estimated using a regression model based on the localized MOEs and knot area ratios (KAR) which were experimentally measured for lamina grades samples. The localized MOE was obtained using a machine stress-rated grader, and the localized KAR was determined using an image-processing system. The bending strength distributions in four types of GLTs were simulated using the developed GLT beam model; these four types included: (1) GLT beams without finger joints; (2) GLT beams with finger joints; (3) GLT beams with different lamina sizes; and (4) GLT beams with different combinations of lamina grades. The simulated bending strength distributions were compared with actual test data of 2.4 and 4.8 m-long GLTs. The Kolmogorov–Smirnov goodness-of-fit tests showed that all of the simulated bending strength distributions agreed well with the test data. Especially, good agreement was shown in the fifth percentile point estimate of bending strength with the difference of approximately 1%.

Performance of glue laminated timber beams composed of sengon wood (Albizia falcatara) and coconut wood (Cocos nucifera) with nylon-threads reinforcement

This paper aims to describe the performance of mix-glue laminated timber beams that are given a nylon strapping as external reinforcement with the three-point bending test to three groups of beams based on the span-to-depth ratio, i.e.: G11, G8, and G5 groups. Each group consists of three types of lamination compositions, namely: Type I, whole lamination consists of sengon wood; Type II, the placement of the coconut wood lamination as the outermost; Type III, similar to type II with added nylon straps with a distance of 5 mm. The bending test results show differences in elastic modulus, flexural strength and shear strength of the glue-laminated timber beams. Based on the comparison of glulam beams consisting of six laminations of sengon wood it was found that the placement of the coconut wood as the outermost lamination succeeded in increasing the elastic modulus, the flexural and shear strength of beams by 28%, 13%, and 34%, respectively. In addition, the reinforcement with nylon straps results in the modulus of elasticity, bending and shear strength of glulam to increase by by 41%, 2%, and 49% respectively.

Computer modeling of glued laminated timber beam reinforced with steel bars fixed with epoxy resin

Structures of glued laminated timber have many technical and economic benefits compared to metal or reinforced concrete: lower weight, sufficient strength and durability. Competent design of such structures requires numerical analysis that best meets specified conditions. This article describes a 3D analysis of a beam composed of glued laminated timber, reinforcement bars and epoxy resin. When determining the stress-strain state of the structure, anisotropic properties of wood were also taken into account. Computer analysis of material behavior of timber, reinforcement bars and epoxy resin was performed with the help of ANSYS software package.

Fire tests on glued-laminated timber beams with specific local material properties

The fire resistance of glued-laminated timber (glulam) beams is usually determined by calculation models or by tests. The evaluation of the fire resistance tests is accompanied by an uncertainty with regard to the timber material properties, which is, however, important to know when comparing the test results to the effective cross-section method according to EN 1995-1-2. The present paper presents therefore for the first time the results of six fire resistance tests with glulam beams with specific local mechanical material properties, such as exact position and dimension of knots, weak sections and finger joints, densities and strength properties of small cells. The tested glulam beams had an approximate height of 250 mm and reached a fire resistance of up to 68 min. The performed fire tests allowed the determination of the zero-strength layer with a higher certainty than investigations performed in the past. Additionally, reference tests at ambient temperature were considered in the evaluation. The determined zero-strength layer was in the range of 7 mm, as given in the current version of EN 1995-1-2 for beams in bending.

Experimental investigation of flexural behavior of glulam beams reinforced with different bonding surface materials

In this study, flexuralbehaviors of glue laminated timber beams manufactured from Pinussylvestristree were investigated by comparing the results with those of massive timber beams. The main variables considered in the study were number of laminations, types of adhesive materials and reinforcement nets used in the lamination surfaces. In scope of the experimental study, glue laminated beams with 5 and 3 lamination layers were manufactured with 90x90mm beam sections. In the lamination process epoxy and polyurethane glue were used. Morever, in order to improve the bond strength at the lamination surface, aluminium, fiberglass and steel wire nets were used at the lamination surfaces. Load–displacement responses, ultimate capacities, ductility ratios, initial stiffness, energy dissipation capacities and failure mechanisms of glue laminated beams were compared with those of massive beams. It was observed that the general bending responses of glue laminated beams were better than those of massive beams. In addition to that the use of reinforcement nets at the lamination surfaces increased the ultimate load capacities of the tested beams. The highest ultimate load capacities were oberved from the tests of glue laminated beams manufactured using five laminated layers and retrofitted with polyurethane glue using steel wire reinforcement nets, in the direction normal to the lamination surface. Finally, the finite element simulations of some test specimens were performed to observe the accuracy of finite element technology in the estimation of ultimate capacities of glue laminated timber beams.

Experimental Study on the Lateral Resistance of Reinforced Glued-Laminated Timber Post and Beam Structures

Nine cyclic tests were conducted on full-scale one-story, one-bay timber post and beam construction specimens to study the lateral resistance of reinforced glued-laminated timber post and beam structures. Two reinforcement methods, wrapping fiber-reinforced polymer (FRP) and implanting self-tapping screws, and two structural systems, simple frame and knee-braced frame, were considered in the experimental tests. Based on the observed experimental phenomena and the test results, the feasibility of the reinforcement was discussed; the contributions of different methods were evaluated; and the seismic performance of the specimens were studied. The results indicated that both reinforcement methods could limit the crack development and improve the strength, stiffness and energy dissipation capacity. The results also showed that the lateral resistance could be significantly improved by retrofitting a failed simple frame with joint reinforcement and a knee-brace, demonstrating that this approach can be applied in engineering practice.

Influences of Scarf-Joint of the Laminae in the Strength and Elasticity of Glued Laminated Timber Beams

The objective of this work is to determinate the influence of the scarf-jointed in the strength and the modulus of elasticity of the glued laminated timber beam. To determine this influence, several tests with the outer laminae with scarf-joint and the bevel with different inclinations has been made. The models were made of Parana Pine, Araucaria angustifolia. For the tests were performed three points bending. With the load values and the deflection at mid-span and by linear regression were determined the effective elastic modulus. The results indicate that the performance is reduced considerably in the presence of a scarf-joint in the external laminae and also the reduction is greater when the scarf angle increases.

Fire Safety of Glued-Laminated Timber Beams in Bending

AbstractDesign models for timber structures with fire-resistance requirements usually take into account the loss in cross section due to charring and the temperature-dependent reduction in strength...

Experimental Bending Behavior of Glue Laminated Timber Beams

The aim of this paper is to prove that glue laminated timber is a viable structural material that can easily replace common steel or concrete beams for small and medium spans. It is a much lighter and eco-friendly material with minimal impact on our eco-system by using significantly less energy in it’s production and also by using timber witch is a sustainable material. Experimental four point loading bending tests were conduced on scaled beams according to the EN 408-2010 [1], tests that were meant to study the behavior of these beams under loading and unloading cycles as well as the bending strength and deflection characteristics.

Comparison of Modulus of Elasticity of Glued Laminated Timber

This article focuses on testing of glued laminated timber beams and researching their properties. The article mainly focuses on comparison of measured modulus of elasticity obtained by two different methods. First method used was method of spike which has non-destructive character. This method was used to measure properties of glued laminated timber (GLT) on macro mechanical level in form of modulus of elasticity. Second method was used to determine micromechanical properties of material and is called nanoindentation. Tested material will be also described the article along with principle of testing and presenting results. Those results of individual measurements will be compared with respect to percentage representation of individual phases on micromechanical levels to measurement on macromechanical level.

Javaslatok rétegelt-ragasztott fatartók tervezéséhez, gyártásához és üzemeltetéséhez, felmérési és modellezési eredmények alapján, III. rész: A tönkremeneteleket igazoló vizsgálatok és eredményei

<p class="p1">A rétegelt-ragasztott fatartók egyre elterjedtebbé váltak az elmúlt 50 évben. A megfelelő minőségű anyagokból készített rétegelt-ragasztott tartók minőségi beszerelést és üzemeltetést követően időtállóak, azonban egyre több esetben fordul elő a rétegelt-ragasztott tartók károsodása és a károsodás miatt egész tetőszerkezetek életveszélyessé válása. Ebben a cikkben a rétegrepedések és tönkremenetelek okaihoz kapcsolódó mechanikai vizsgálatok és azok eredményei kerülnek bemutatásra.<br /> A mechanikai vizsgálatok célja, hogy próbatest szinten megállapítsuk a ciklikusan változó klimatikus környezet (hőmérséklet, páratartalom) hatását az RR tartók faanyagára és annak ragasztási síkjaira. Mivel a faanyag rostra merőleges húzószilárdsága és nyírószilárdsága csekély, a tartókon kialakult delamináció oka, ezen feszültségek szilárdságot meghaladó mértékében keresendők. Az elvégzett vizsgálatok is a két szilárdság meghatározására ill. a ciklikusan változó klimatikus környezet ezen szilárdságokra gyakorolt hatására irányultak.</p>

Mechanical performance of glued-laminated timber beams symmetrically reinforced with steel bars

The technology of glued laminated (glulam) timber has enabled the design of composite structures with large dimensions. The laminations are generally derived from the sawing of small trees and species of rapidly growing, which yields laminates with low mechanical properties. This study evaluates the benefits of the reinforcement of glulam beams, by employment of steel reinforcement ratios of 2% and 4%. In the beams with a ratio of reinforcement of 2%, in relation to the unreinforced glulam beams, the stiffness increased approximately 52% and the serviceability load increased 53.1%, and with the employment of steel ratio equal to 4% these increases were in the order of 73% and 79.2%, respectively. The results showed that the insertion of steel bars can reduce the inherent variability of wood and increase significantly the stiffness of glulam, which consequently increases the beam capability for serviceability limit states.

Pulse Method Used for Non-Destructive Assessment of Glued Laminated Timber Beams

This text is focused on GLULAM (glued laminated timber) beams and determination of their properties. This text is mainly focused just on part of more complex research of glued laminated timber beams. This text is focused on pulse method, which is used to determine the dynamic modulus of elasticity of GLULAM beams. This text will describe how the pulse method works, with basic description, describes the tested material and compare the results of testing. In the conclusion we discuss the results, make conclusions and describe the way of our further research of glued laminated timber beams.

Creep of GLT Beams during Four-Point Bending Test

The present work is concerned with the evaluation of creep deformation developed during the four-point bending test of glued laminated timber beams. In particular, three deflections (at the mid-span of the beam, and below the points of load application) were recorded for each tested beam. The time variation of deflections at 110 loading levels was examined in details for the set of five beams. It can be seen that the effect of creep covers about 10 – 20% of the overall strain. To proceed with numerical simulations requires, however, building first a reliable computational model that agrees well with purely elastic response of the beam. Thus additional measurements were carried out assuming a rather short hold period to eliminate the creep effects. The results were then compared with numerical simulations promoting the computational model to be used in more advanced simulations incorporating a suitable rheological model.

Non-Destructive Testing of Glued Laminated Timber Beams with Use of Pilodyn 6J – Method of Spike

This article is focused on GLULAM (glued laminated timber) beams and determination of their properties by using non-destructive method. This text is mainly focused just on part of more complex research of glued laminated timber beams. This text is focused on non-destructive method, which is the method of spike that uses device called Pilodyn 6J for measurement. Results of this method are in form of Young ́s modulus of elasticity. This article will describe how the method of spike works, with basic description, describes the tested material and compare the results of testing. In the conclusion we discuss the results, make conclusions and describe the way of our further research of glued laminated timber beams.

Application of stochastic finite element approaches to wood-based products

Due to the natural growing process of wood, the mechanical properties of wooden boards are subject to high variability, mainly introduced by knots and the resulting deviation of the wood fibre directions around them. This variability has a great impact on the serviceability limit state performance of wood-based products, such as glued-laminated timber, and thus should be considered within design concepts. Numerous applications of random process models for numerically representing the fluctuation of the mechanical properties along wooden boards can be found in the literature. But, the corresponding mechanical probabilistic investigation, however, is limited almost exclusively to Monte Carlo simulations so far. For this reason, the focus of this work is laid on alternative probabilistic approaches, in particular the perturbation and the spectral stochastic finite element method. Both methods are combined with several discretization methods for the random process, programmed in a consistent environment, and compared to the Monte Carlo simulation, regarding computational effort as well as quality of results. For this purpose, the second-order moments (mean and standard deviation) of the system response of a glued-laminated timber beam with random lamination stiffness are computed. The performance of the different approaches is compared and, in particular, the influence of the variability of the ‘raw’ material on the structural response is shown. Well-known effects, such as the decrease in the variability of effective properties of GLT with increasing number of lamellas, are numerically reproduced and quantified. Moreover, a significant influence of the correlation length, specifying the rate of material property fluctuation within each lamella, on the effective stiffness of the resulting glued-laminated timber beams is demonstrated.